Radio frequency (RF) signal generators produce test signals that simulate operating conditions in a variety of electronic systems. For example, signal generators provide amplitude, pulse and frequency modulated test signals for simulating target returns and antenna scan-patterns in radar systems. To simulate time-slot to time-slot changes in power levels of signals received by time domain multiple access (TDMA) cellular base stations, or to test squelch circuits and automatic gain control (AGC) circuits in receivers, it is desirable that the signal generator provide test signals having amplitudes that rapidly change between two precisely defined power levels. Unfortunately, slow response time of automatic level control (ALC) loops and electromechanical step attenuators in presently available signal generators impair the ability of the signal generators to provide this type of amplitude-adjusted test signal.
One system that rapidly adjusts the amplitude of a test signal between two precisely defined power levels incorporates two signal generators and a high speed switch. Each of the signal generators is set to a different power level and the switch rapidly connects either of the signal generators to an output. The power level of the test signal is dependent on which of the two signal generators is connected to the output. Although this system has high accuracy and high amplitude switching speed, use of two signal generators makes this type of system expensive, and separate control of the signal generators and the switch is cumbersome.